Bump trillian-opensource-ci/db_server in /config/trillian/mysql (#1784)

Bumps trillian-opensource-ci/db_server from `834c7fe` to `d0839b2`.

---
updated-dependencies:
- dependency-name: trillian-opensource-ci/db_server
  dependency-version: d0839b263dcefbb484320988f7ee257492582612989f6a732b62be037f667261
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

config/trillian/mysql/300-mysql-trillian.yaml

@@ -20,7 +20,7 @@ metadata:
     app: mysql-trillian
 spec:
   containers:
-    - image: gcr.io/trillian-opensource-ci/db_server@sha256:834c7feedb271f454f65c0978f38fb6809b99f020ebe8126f0d4029ce7055733
+    - image: gcr.io/trillian-opensource-ci/db_server@sha256:d0839b263dcefbb484320988f7ee257492582612989f6a732b62be037f667261
       name: mysql
       env:
         - name: MYSQL_ROOT_PASSWORD